Anti‐Stokes Fluorescence and Nonlinear Optical Properties of the Functionalized Phenoxazine‐based Dye: A computational study

Abstract

Tuning of electronic, photophysical and nonlinear optical (NLO) properties of the phenoxazin‐3‐one dye, resazurin (Rz), is here attempted through functionalization by employing the electron‐donating and electron‐withdrawing groups. Density functional theory (DFT) and time‐dependent DFT calculations were performed for the purpose. Examining the absorption‐emission spectra, featuring an intense band (ππ*) followed by a weak band (nπ*), of the functionalized dye derivatives reveal the Stokes shift, and relatively a large shift is found for the cyano‐functionalized Rz molecules. Surprisingly, the 2‐mono‐cyanoresazurin shows the anti‐Stokes fluorescence (ASF) emission induced by the hot‐band absorption, and at the other end, the weak absorption band associated to the charge transfer nπ* transition of the nitro‐functionalized molecules is being quenched. Radiative lifetime analysis infers that the pull‐type functionalized molecules decay slowly whereas the push‐type shows the high emission rate. The structure‐property relations between the molecular parameters were also discussed. Tuning the NLO properties infers that the pull‐type group exhibits significantly high hyperpolarizabilities (for cyano‐) whereas the push‐type exhibits relatively small β‐value (for amino‐) when compared the standard NLO molecule. Here, the tetra‐functionalized‐Rz molecules may act as promising candidates for NLO applications, and also probing their ASF emission further unfolds the bio‐applications.